The invention relates to a turbine wheel in an exhaust gas turbine of an exhaust gas turbocharger with a wheel hub and a plurality of blades arranged on the wheel hub and extending axially between the turbine inlet and the turbine outlet.
The document DE 102 12 032 A1 discloses an exhaust gas turbocharger for an internal combustion engine, composed of a compressor in the intake section of the internal combustion engine and an exhaust gas turbine in the exhaust section, said turbine being driven by the pressurized exhaust gases, the rotational movement being transmitted to the compressor wheel which subsequently compresses ambient air to a raised charge pressure which is fed to the cylinders of the internal combustion engine. A variably adjustable guide grating is mounted in the turbine inlet cross section, upstream of the turbine wheel of the exhaust gas turbine, as a result of which the effective turbine inlet cross section can be set to a desired value as a function of the current operating state of the internal combustion engine. As a result, the behavior of the internal combustion engine can be optimized both in the engine braking mode and in the fired drive operating mode. In the engine braking mode, the guide grating is moved into a choked position which reduces the flow inlet cross section and as a result of which the exhaust gases are choked upstream of the exhaust gas turbine and the internal combustion engine has to perform additional compressor work counter to the raised exhaust, which leads to a significant increase in engine braking power. In contrast, in the fired drive operating mode the guide grating is adjusted to an open position which makes the flow inlet cross section larger, in order to increase the power of the engine so that a maximum throughput of exhaust gas through the exhaust gas turbine is possible.
During high engine braking power operation, the turbine wheel is stressed to a maximum when the engine is operated in the engine braking mode. The high exhaust gas back pressure leads, in conjunction with the reduced flow cross section, to high speed compression surges which can destroy the turbine wheel blades when the surges strike the turbine wheel. In order to avoid such destruction it is necessary to ensure that the turbine wheel blades are not excited to oscillate in any way up to the region of their first natural frequency since otherwise the risk of fracturing would substantially increase. In order to counteract this, it is possible, for example, to increase the thickness of the turbine wheel blades. However, this entails an undesired increase in the mass inertia, as a result of which the transient behavior of the exhaust gas turbocharger would deteriorate. Furthermore, the turbine would less willingly accelerate, which is needed for increasing the engine power, output and particularly in the engine braking mode.
U.S. Pat. No. 5,094,587 discloses an exhaust gas turbocharger for an internal combustion engine having a compressor in the intake section and an exhaust gas turbine in the exhaust section of the engine. The turbine wheel is driven by the exhaust gases of the engine which are expelled under pressure, the rotational movement of the turbine wheel being transmitted via a shaft to the compressor wheel which subsequently sucks in ambient air and compresses it to a raised charge pressure which is fed to the inlets of the internal combustion engine. In the turbine housing of the exhaust gas turbine, two exhaust gas flows are formed, via each of which exhaust gas is fed to the turbine wheel. The two exhaust gas flows open into a semi-axial or semi-radial position onto the turbine wheel blades which are arranged on the turbine wheel hub. The exhaust gas of the exhaust gas flows which impacts on the turbine wheel blades in the semi-axial or semi-radial direction is deflected in the turbine wheel into an axial flow and leaves the turbine wheel axially. In order to be able to absorb the high loads which occur during operation at the high rotational speeds, the turbine wheel blades have an increased thickness in the region of the connection to the turbine wheel hub.
It is the object of the present invention to provide, with simple measures, a turbine wheel in an exhaust gas turbine of an exhaust gas turbocharger which is configured for a long service life and to withstand high power levels as they may be present in particular in the engine braking mode of operation.